A reflector utilizing pre-stressed elements



May 23,1961 H. HOLLAND ET AL REFLECTOR UTILIZING PRE-STRESSED ELEMENTS 2Sheets-Sheet 2 Filed Dec. 5, 1958 INVENTOR. HERMAN HOLLAND ROBERT e.SIMONEAU X/M' ATTORNEYS United States Patent A REFLECTOR UTILIZINGPRE-STRESSED ELEMENTS Herman Holland, 957 Albion St., and Robert G.Simoneau, 3702 Delmar Ave., both of San Diego, Calif.

Filed Dec. 5, 1958, Ser. No. 778,544

14 Claims. (Cl. 343 912) The present invention relates to a reflector,and more particularly to a reflector for use in reflecting light, heat,and similar forms of energy, such as electromagnetic waves in long rangesearch, detection, and guidance equipment.

In order to obtain maximum utilization of recent and continuingimprovements in electronic gear for propagating and receivingelectromagnetic waves, it has become necessary to provide very large andaccurate reflector assemblies. It is also necessary that thesereflectors have a minimum deflection under load in order to provide thedesired accuracy. Large diameter, minimum deflection reflectors arediflicult and expensive to construct using present day techniques sinceit is characteristic of present space framework structures that theymust be massive and heavy to reduce deflection to a satisfactory degree.These structures are often as great as 120 feet or more in diameter, andas they become larger the framework must become heavier to reducedeflection. As the size increases, the deflection problem becomes moreacute, necessitating the use of heavier bracing structures, until apoint of diminishing returns is reached, that is, when the dead weightof the structures becomes so great that its weight alone causesexcessive deflections. In addition to this dilemma, the great weight ofthe structure imposes severe stresses upon the gimbal bearingssupporting the reflector, and requires heavy counterbalancing andconsiderable power to operate the reflector. These problems are furtheraggravated because the current trend is toward the use of higherfrequencies which require a continuous reflector face surface, ratherthan the open face or grid framework now in use with lower frequencies.This imposes higher wind and ice loads upon the backup or supportstructure, requiring still more heavy bracing to reduce the deflectionto an acceptable level.

Accordingly, the present invention provides a reflector which has a veryaccurate reflective surface and which is extremely efiicient from aweight-deflection standpoint. The reflector also is characterized byeconomy of manufacture, logistic simplicity, and ease of maintenance.The reflector is made up of several groups of parts which areinterchangeable within their group so that an essentially modular designis provided. Essentially, the reflector comprises a plurality of ringswhich are arranged in adjacent spaced relationship, and which aresecured together by a plurality of circumferentially spaced tensionelements secured between adjacent rings. In addit-ion, a continuousface, curved reflecting surface is arranged upon the edges of theplurality of rings. The rings are preferably made in sections andsecured together by fasteners which are quickly installed and removed.The rings are supported and stabilized by the plurality of tensionelements, which may be rods or wires or the like, so that the rings andthe rods form a back-up structure for the continuous face or solidreflector surface. This surface is constructed of a plurality of panels,preferably made of sandwich construction, which are individuallyadjustable at their corners, individually removable and replaceable, andadapted'to act as non-load bearing members, except in their function oftransmitting wind and ice loads into the back-up structure. That is, thepanels do not serve to any appreciable extent in tying together orbracing the assembled rings and tension rods. The rings are secured indesired position by adjusting the lengths of the rods, and the wholeback-up structure is prestressed by tightening the tension rods; Suchprestressing takes up the bulk of the manufacturing and assemblytolerances, and insures that the structure will be capable ofwithstanding erection and operating loads without exceeding apredetermined acceptable deflection. It is also noted that adjustment ofthe lengths of the tension rods will properly align the reflector facepanels to a desired shape, such as an accurate parabolic shape. Theadjustment of the panels at their four corners permits a fineradjustment of the position of each panel so that a high degree ofaccuracy in forming a parabolic face is afforded.

Although the description hereinafter made will be directed to theemployment of a plurality of solid face panels to'form the reflectorsurface, it will be apparent that the back-up structure of the presentinvention is also adapted to carry a conventional mesh or open facereflector surface.

The compression ring members are preferably made of sandwich panels, andcan be fairly thin in section since most of the stress imposed upon'themis in hoop tension and hoop compression. The fact that the reflectorface panels do not carry any of the primary stress of the structuremakes it possible to locally adjust any of these panels withoutdisrupting the position of any of the other panels and without affectingthe stress in any part of the primary or backup structure. Theprestressing of the rods or tension members insures that none of suchmembers will be placed in compression under any conditions ofunsymmetrical loading. This in turn means that all tolerances taken upby the prestressing will be substantially eliminated under even the mostsevere conditions of operational loading. Further, since each rod orstrut is always in tension, it will be working under all loadingconditions, with a resulting gain in structural efliciency.

Other objects and features of the present invention will be readilyapparent to those skilled in the art from the following specificationand appended drawings wherein is illustrated a preferred form of theinvention, and in which:

Figure 1 is a plan view of the reflector side of the antenna of thepresent invention, portions being cut away to illustrate theunder-structure thereof;

Figure 2 is a view taken along the line 2-2 of Figure 1;

Figure 3 is a detail view illustrating the manner of securing togetheradjacent segments or panels of a ring;

Figure 4 is a partial perspective view illustrating the channelconstruction at the upper and lower edges of the ring segments, and alsoillustrating the manner of securing the tension tie rods thereto;

Figure 5 is a partial perspective view illustrating the adjusting meansfor aligning individual panels in position upon the upper edge of aring; and

Figure 6 is a detailed view illustrating one means for effectingelectrical interconnection between adjacent panels.

Referring now to the drawings and in particular to Figures l and 2,there is illustrated an antenna reflector, generally designated 10,which is adapted for the transmissionor reception of electromagneticwaves.

Reflector comprises, generally, a series of concentric compression bandsor rings 12, 14, 16, 18 and 20. These rings are preferably made insections so that they may be easily assembled in situ, and are arrangedin axial, concentric fashion and slightly offset from each other to forma parabolic shape at their reflector or outer edges. The rings aresupported and stabilized in position by a plurality of tension elementsor rods 22. As will be seen, the plurality of concentric rings,stabilized in position by rods 22, serve as the back-up or supportingstructure for a solid reflector surface which ismade up of a pluralityof reflector panels 24. Each of these panels 24 is individuallyadjustable at its four corners, individually removable and replaceable,and do not act as load-bearing members, except in their function oftransmitting wind and ice into the back-up structure. Rods 22 arepreferably prestressed to a level high enough to insure that mostmanufacturing and assembly tolerances will be taken up. In this wayantenna 10 is inherently adapted to withstand erection and operatingloads without exceeding a predetermined acceptable deflection. Onceconstructed, individual adjustments at the corners of the panels permitthe panels to be arranged in an accurate parabolic shape, as desired.Throughout the description hereinafter to be made it will be apparentthat reflector 10 is made up of several groups of identical parts whichlend themselves to economy of manufacture, ease of shipment andhandling, and simplicity of assembly, erection and maintenance.

More particularly, each of the bands or rings 12, 14, 16, 18, and takesthe form of a cylindrical band which by reason of its continuous naturetransmits loads throughout the periphery of the rings. The number ofrings, their spacing, and their size may be varied to suit theparticular loading conditions of each application. Each of the rings ismade up of a plurality of individual, and preferably identical, ringsegments or panels 19, Figure 4, which are preferably of sandwichconstruction. That is, to attain a high strength-to-weight ratio thepanels 19 preferably comprise a structure formed of honeycomblike corematerial arranged in edgewise relation between a pair of parallel facingskins, as illustrated. The core and skins are secured together, as byadhesive bonding or welding, to produce a strong and lightweightcomposite structure. However, if desired, panels 19 may be made of othermaterials also, if desired.

Panels 19 may be curved to produce a perfectly round ring when they aresecured together, but for manufacturing simplicity they are preferablymade rectangular and flat. This produces a ring which is a many sidedpolygon, but which is for all practical purposes round. The number ofpanels in each of the rings will, of course, vary, depending upon theperipheral length of each panel and the size of the ring to be produced.

The adjacent side edges of panels 19 are detachably secured together byany suitable means, such as by a pair of piano-type hinge fittings orconnections 26, one on the inner and one on the outer side of each paneladjacent its edges, Figure 3. Connections 26 are secured to panels 19 byany suitable means, such as by bolts 27 or the like threaded into femalefittings anchored in the core portion of each panel 19. A pin 28 isprovided to couple together the hinge portions of connection 26 so thatthe various panels 19 may be quickly assembled by merely driving pins 28into position. It is to be noted that since each panel 19 issubstantially identical to every other panel 19 in its respective ring,there is no necessity for identifying the individual panels for assemblypurposes.

The various rings are formed by assembling the respective panels 19 inthe manner described, and the rings are arranged in the concentricfashion illustrated in Figures 1 and 2, the inner rings beingprogressively offset along the axis of the assembled rings to producethe desired reflector shape. Thus, for a parabolic reflector shape, theouter edges of the various rings will form a support which is adapted toform a parabola when they are covered by reflector panels, as will beseen.

The plurality of continuous bands or rings are secured together bytension elements or rods 22, the lengths of rods 22 being made such thatthey will support and maintain the rings in the offset positions justdescribed. Rods 22 are then prestressed to maintain these positions witha minimum of deflection.

Referring now to Figure 4, there is illustrated the manner of attachmentof rods 22 to each of the ring segments or panels 19. For purposes ofillustration, the attachment of rods 22 will be described in connectionwith a typical ring 16, it being understood that the connections aresubstantially identical for each of the other rings.

The individual panel components or segments 19 of ring 16 are cut awayor routed out at their upper (forward) and lower (rearward) edges toaccept a pair of U-shaped channels 30, respectively, which are rigidlysecured in position by bonding to the inner faces of the facing skins ofpanels 19. That is, the core edge portions of panels 19 are routed outto make room for channel 30, and the channel is then bonded to theskins. Each channel 36 is also secured in position by a plural ity ofpairs of bolt and nut assemblies 32, the bolts thereof being disposedthrough spacers or bushings 34 located within the interior of channel30. Each channel 30 may thus be firmly clamped to the skins of eachpanel 19 without crushing of either.

Assemblies 32 also secure a pair of substantially C- shaped channels 36in position against panels 19, channels 36 forming the upper and loweranchorages for the ends of rods 22, as will be seen. The lower flange ofeach upper channel 36 is provided with a plurality of pairs of spacedopenings for accepting the plurality of nut and bolt assemblies 38 forsecuring the clevises 40 of tension rods 22 in position. Although Figure4 illustrates only the upper channel 36 and the upper ends of rods 22,it will be understood that the lower ends of these rods 22 are alsosecured in similar fashion to the upper flange of the lower channel 36of the next adjacent rings, in this case the rings 14 and 18. A rod 22is connected between the upper corner of a ring panel 19 of ring 16 andthe lower diagonally opposite corner of a panel 19 of an adjacent ring.The other upper corner of the same panel 19 of ring 16 is connected tothe other lower corner of the panel 19 of an adjacent ring. In this waythe pair of rods 22 are diagonally disposed, and intersect in X fashionbetween the upper corners of the panel of ring 16 and the lower cornersof the panel of the adjacent ring. In similar fashion, a pair of rods 22are connected between the lower corners of the same panel 19 of ring 16and the upper corners of the panel 19 of the adjacent ring, these rods22 also crossing each other in diagonal fashion. This same arrangementis repeated for each pair of confronting panels 19 about the peripheryof ring 16 and the adjacent ring, and the same arrangement is followedfor confronting panels 19 of the other rings also. It will be apparentthat slightly different arrangements of rods 22 can be devised foreffecting the same function, so long as the rods 22 are prestressed andact to distribute loads throughout the various rings.

A means for generating tension in rods 22 is necessary to prestress rods22 to take up residual tolerances,

and for this purpose a turnbuckle 42 or the like is provided in each rod22. Rotation of turnbuckle 42 in the as is well known in the art. Aspreviously mentioned,

wires or like tension elements could be used as an alternateconstruction instead of rods 22.

The curved or parabolic reflecting surface for antenna is provided byarranging a plurality of panels 24 in adjacent relationship, andsecuring them to the upper flanges of the plurality of channels 36 ofthe various concentric rings. It is to be understood, however, that thepanels 24 do not provide any appreciable support for the back-upstructure comprising the rings and rods 22, but are merely positionedfor affording the desired electromagnetic wave reflection. Theirdisposition is primarily dictated by the relative height of the variousrings, which in turn is controlled by the lengths and pre-tension forcesin rods 22, but there will also be described a means for effecting asecondary and more precise arrangement of the panels 10.

The means for enabling a precise adjustment of the position of eachpanel 24 comprises, Figure 5, a splice plate 44 which is arrangedadjacent the upper or forward flange of the adjacent channel 36. Spliceplate 44 is provided with four positioning assemblies 46, whereby it isadapted to provide a support for the corners of four panels 24. Thecorner of each panel 24 rests upon a disc-like head 48 of one of theassemblies 46, and the relative height of that corner of panel 24 withrespect to plate 44 is adjusted by rotating a pair of nuts 50 along athreaded shank which is integral with head 48. Once the proper height isachieved, nuts 50 are rotated until they firmly abut against thesurfaces of plate 44 to thereby lock head 48 in position. At this pointthe corner of panel 24 is merely resting upon the upper surface of head48, and to secure panel 24 in this adjusted position, a bolt 52 isdisposed through that corner of panel 24, through plate 44, and thencethrough the upper flange of channel 36. A nut 54 is next threaded uponthe end of bolt 52 to secure panel 24 in position. Thus it will be seenthat although the position of panel 24 is roughly located by thepreviously established height of the adjacent ring 16, a fine or Vernieradjustment of the height of panel 24 may be provided by manipulating thevarious assemblies 46. It will be understood that many plates 44 areemployed in this same fashion about the upper or forward rim peripheriesof the various rings so that all panels 24 are secured at their fourcorners in precise positions established, first by the locating of therings at their proper heights through adjustment of the lengths of rods22, and second by manipulating the positioning assemblies 46. a

The various panels 24 are preferably constructed of sandwich material,as described hereinabove with respect to panels 19, but panels 24 may beconstructed of open face mesh or other material, if desired. The use ofsandwich material in the present invention is preferred because of thehigh strength-to-weight ratio of that type of construction, but thereare no doubt situations where an open face material would be desired,and the novel back-up structure of the rods and rings, as herein taught,is equally adapted to support and position such an alternativeconstruction.

The shape of panels 24 is, of course, dictated by the desired shape forthe reflecting surface of reflector 10, but for the parabolic reflectingsurface herein contemplated each panel 24 is provided with substantiallyparallel upper and lower edges, except for the innermost panels 24,which will be slightly arcuate in shape to conform with the contour ofthe upper edges of the rings. The side edges of panels 24 will betapered inwardly to permit them to be fitted as wedges or petals in theoverall assembly, the taper becoming greater for the panels which arelocated in the innermost positions. In addition, reflector panels 24will be substantially flat, although a slight curvature may be providedto give a more accurate parabolic shape. It will be apparent that thediameter of reflector 10 will largely dictate the shape of reflectorpanels 24 since, as the diameter becomes larger,

reflector 10 is left uncovered in the present embodiment.

A sub-reflector, feed horn, or similar propagating or receivingequipment (not shown) may be mounted for-' wardly of the main reflectingsurface of reflector 10, and portions of a plurality of struts 56 forthis purpose are illustrated in Figures 1 and 2. Each strut 56 isconnected at the rearward end to ring 20 in any suitable manner, such asby being bolted to a fitting 58 which is rigidly secured to ring 20. Insimilar fashion a plurality of gimbal struts 60 are bolted or otherwisesecured to the rearward ends of fittings 58 and are connected (notshown) to a gimbal mount for supporting reflector 10 in position. Thegimbal mount and the means of mounting reflector 1t) thereto are notimportant to the present invention, and will therefore not be describedin any particular detail, other than to note that the gimbal mounttogether with usual and conventional apparatus associated therewith isoperative to cause reflector 10 to track in azimuth and elevation.

Electrical continuity between reflector panels 24 may be provided bycontrolled gaps between the panel edges for capacitance conduction, asis well known, or, as is best illustrated in Figure 6, may be providedby affixing a thin, flexible, metallic, non-structural tape or strip 62to the edges of adjacent panels 24. This can be done by installingself-tapping metal screws, by adhesive bonding techniques, or by anyother means suitable to effect electrical interconnection between panels24 and strips 62.

From the description hereinabove made it will be seen that a reflector'10 has been provided which is extremely light in weight, the back-upstructure thereof comprising concentric, continuous, sectional sandwichcompression rings, supported and stabilized by substantially radiallydisposed inter-ring rods 22 which have been prestressed to reducedeflections of reflector 10 under load. The reflector surface is alsolight in weight, being constructed of sandwich reflector panels 24, andis accurate in contour, the contour thereof being precisely adjustableby manipulating positioning assemblies 46 until panels 24 are in theprecise positions desired. In addition, the pro-stressing of rods 22stabilizes the assembly, and substantially all tolerances in fittingsand attachment members will be taken up prior to operational loading.

While certain preferred embodiments of the inven-. tion have beenspecifically disclosed, it is understood that the invention is notlimited thereto as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation Within the terms of the following claims.

I claim:

1. A reflector comprising: a plurality of endless structure means, eachbeing generally cylindrical in configuration, said plurality ofstructure means being arranged in adjacent, spaced relationship, saidstructure means having different diameters, the front edge of the innerstructure means being arranged rearwardly of the front edge of the outerstructure means; a plurality of circumferentially spaced tensionelements secured between said structure means, certain of said tensionelements each having one end connected adjacent the front edge of theouter structure means and the other end connected adjacent the rear edgeof the inner structure means, and certain of said tension elements eachhaving one end connected adjacent the rear edge of the outer structuremeans and the other end connected adjacent the front edge of the innerstructure means; a plurality of means carried by and operative upon saidtension elements, respectively, to individually and adjustably prestresseach said tension element whereby assembly tolerances are taken up andwhereby each said tension element is in tension under load; and areflecting surface means arranged adjacent the forward edge portions ofsaid structure means.

2. A reflector according to claim 1 and characterized in that saidtension elements are rods.

3. A reflector according to claim 1 and characterized in that saidtension elements are wires.

4. A reflector according to claim 1 and characterized in that saidtension elements are elongated braces, and in that said last-mentionedmeans are operative to shorten the length of said braces to therebycreate a prestressed condition in said braces and thereby orient saidstructure means.

5. A reflector for electromagnetic waves comprising a plurality ofconcentrically spaced cylindrical rings, each of said rings having arearward rim and a forward rim; a plurality of circumferentially spacedtension elements secured between the adjacent rings and adjacent theforward and rearward rims thereof, certain of said elements extendingbetween the forward rim of one of the adjacent rings and the rearwardrim of the other of said pair of adjacent rings, and certain of saidelements extending between the rearward rim of said adjacent rings andthe forward rim of said other adjacent rings; means operative upon eachsaid tension element to prestress said tension element whereby assemblytolerances are taken up and whereby said tension element will be intension under load; and a reflecting surface arranged adjacent theforward rims of said rings.

6. A reflector according to claim 5 and characterized in that saidtension elements are rods.

7. A reflector according to claim 5 and characterized in that saidtension elements are wires.

8. A reflector according to claim 5 and characterized in that saidtension elements are longitudinally extending braces and in that saidmeans are operative for shortening the length of the brace to therebycreate a prestressed condition in said brace.

9. A reflector for electromagnetic waves comprising a plurality ofconcentrically spaced cylindrical rings, each of said rings including aplurality of substantially rectilinear panel sections interconnected attheir side edges; a plurality of circumferentially spaced tensionelements secured between the adjacent rings, a separate one of saidtension elements being secured between each corner of each said panelsection of one of the rings and the diagonally opposite corner of eachconfronting panel section of an adjacent ring; said tension elementsincluding means for imparting tension loads in said tension elements forprestressing the assembled said tension elements and said rings; areflecting surface arranged adjacent the forward edges of said rings.

10. A reflector for electromagnetic waves comprising a plurality ofcontinuous cylindrical members arranged one within the other in adjacentspaced relationship, the

forward rims of said'members being axially offset; a reflecting surfacearranged "over said forward rims to form a reflecting dish section; anda plurality of diagonally disposed elements secured between adjacentmembers, said elements including means for imparting tension loads insaid elements for prestrcssing the assembled said members and saidelements.

11. A reflector according to claim 10 and characterized in that saidcylindrical members are each comprised of a plurality of edge connectedpanels of sandwich construction.

12. A reflector according to claim 10 and characterized in that saidreflecting surface is comprised of a plur'ality of reflector panels ofsandwich construction, each of said panels bridging at least a pair ofsaid cylindrical members.

7 13. A reflector according to claim 10 and characterized in that saidreflecting surface is comprised of a plurality of reflector panels ofsandwich construction, each of said panels bridging at least a pair ofsaid cylindrical members, and in that said reflector panels areelectrically interconnected by thin, flexible metallic strips.

14. A reflector for electromagnetic waves comprising a plurality ofcontinuous cylindrical members arranged one within the other in adjacentspaced relationship, the forward rims of said members being axiallyoffset; a plurality of diagonally disposed elements secured betweenadjacent members for maintaining said members in position; a reflectingsurface arranged over said forward rims to form a reflecting dishsection, said reflecting surface including a plurality of reflectingpanels having portions disposed over said forward rims; and meansconnected between said forward rims and said portions of said panels foradjusting the spacing therebetween whereby the contour of saidreflecting surface may be accurately adjusted.

References Cited in the file of this patent UNITED STATES PATENTS1,938,799 Bourne Dec. 12, 1933 2,298,880 Gartenmeister Oct. 13, 19422,471,828 Mautner May 31, 1949 FOREIGN PATENTS 989,286 France May 23,1951 OTHER REFERENCES Pub. II-Crom, Engineering News-Record, April 16,1936, page 555.

Pub. I, Architectural Record, September 1956, pp. 211-216.

